chemistry

• Atoms are the different types or elements represented in the periodic table by a symbol
• Compound


  A substance that contains two or more different types of atoms chemically bonded together
• For every one oxygen atom there are two hydrogen atoms
• If there's no number after a symbol, there's an invisible one
• Chemical reaction


  Atoms change what they're bonded to and how they're bonded
• Representing a reaction


  1. Word equation

  2. Chemical equation using symbols
• Atoms are not created or destroyed in any chemical reaction, there must be the same number of each type of atom on both sides
• Balancing a chemical equation

  1. Start with atoms only in compounds

  2. Use numbers in front of elements or compounds to multiply them up
• For an element in a reaction, we always finish balancing that as there's no knock-on effect
• Mixture


  Any combination of any different types of elements and compounds that aren't chemically bonded together
• Solution


  A mixture of a solute (solid dissolved in a liquid) and a solvent
• Separating a mixture


  1. Filtration (for large insoluble particles)

  2. Crystallization (to leave a solute behind after evaporating the solvent)

  3. Distillation (to separate liquids with different boiling points)
• These are all physical processes, not chemical reactions, as no new substances are being made
• Formulation


  A mixture that has been specially designed to be useful in a very specific way with very specific quantities of different substances
• Chromatography


  A way of separating substances in a mixture by using a stationary phase and a mobile phase
• Chromatography


  1. Draw a line at the bottom in pencil

  2. Measure how far the solvent has moved and how far the substance(s) have moved

  3. Calculate an RF value (retention factor) as a ratio of how far a spot has moved compared to the solvent
• States of matter


  • Solid (particles vibrate around fixed positions)
  • Liquid (particles are still touching but free to move past each other)
  • Gas (particles are far apart and move randomly with the most energy)
• Gases can be compressed, while solids and liquids cannot
• Melting or evaporating a substance


  Supply energy, usually in the form of heat, to overcome the electrostatic forces of attraction between the particles
• Melting, evaporating, and other physical changes do not make new substances, they are physical changes not chemical reactions
• State symbols


  s for solid, l for liquid, g for gas, aq for aqueous (dissolved in solution)
• Atom


  • Made up of positive and negative charges (JJ Thompson's Plum Pudding model)
  • Positive charge is in a small nucleus, with electrons orbiting relatively far away (Rutherford's discovery)
  • Electrons exist in shells or orbitals (Niels Bohr's discovery)
  • Nucleus contains protons (positive charges) and neutrons (neutral charges) (James Chadwick's discovery)
• Protons and electrons


  Have equal and opposite charges, relatively speaking protons and neutrons have a mass of 1, electrons have a very small mass
• Periodic table


  • Tells us everything we need to know about an atom
  • Bottom number is the atomic number (number of protons)
  • Top number is the mass number or relative atomic mass (protons + neutrons)
• Isotopes


  Atoms of the same element but with different numbers of neutrons
• The average relative atomic mass on the periodic table accounts for the relative abundance of different isotopes
• Electron configuration


  Electrons exist in shells around the nucleus, with a maximum of 2, 8, 8, 2 electrons in each shell
• Metals and non-metals


  • Metals are to the left of the staircase on the periodic table, they donate electrons
  • Non-metals are to the right of the staircase, they accept electrons
• Groups on the periodic table

  • Group 1 (alkali metals)
  • Group 7 (halogens)
  • Group 0 (noble gases)
• Reactivity of groups


  • Alkali metals get more reactive down the group as the outer electron is further from the nucleus
  • Halogens get less reactive down the group as the outer shell is further from the nucleus
• Ion formation


  • Metals form positive ions by losing electrons
  • Non-metals form negative ions by gaining electrons
• The charges of all ions in an ionic compound must add up to zero
• Ionic bonding


  Forms between a metal and a non-metal, where the metal donates electrons and the non-metal accepts them
• Ionic compounds


  Consist of lots of repeating units of ions in a lattice, have high melting and boiling points, can conduct electricity when molten or in solution
• Molecular ions


  Consist of a group of atoms bonded together and carrying a charge, e.g. OH-
• Covalent bonding


  Forms between non-metals, where they share electrons to gain full outer shells
• Simple molecular/covalent structures


  Individual molecules that can mix together, have relatively low boiling points
• Giant covalent structures


  One continuous network of covalent bonds, e.g. diamond and graphite, have very high melting and boiling points
• Allotropes


  Different structural forms of the same element, e.g. diamond and graphite are allotropes of carbon
• Nanoparticles


  Structures between 100-2500 nanometers in size, have a very high surface area to volume ratio